When leaves of a citrus tree curl evenly along their length, this is a protective response to minimises leaf surface area in order to reduce moisture loss. It indicates that the roots of the tree can’t supply enough water to support the leaves.
This form of leaf curling may be due to temporary conditions, such as:
- Lack of irrigation, where the soil has run dry because the tree has not received sufficient watering.
- Heat stress, where high temperatures and strong winds are stripping moisture from the tree faster than the roots can resupply water from the soil.
These are simply conditions of water stress, from which the tree recovers when water is resupplied or extreme weather subsides.
It may also be due to more permanent conditions, such as:
- Prolonged drought conditions where the soil has become so dry the roots have begun to die off.
- Excessively wet or boggy soil conditions which have caused the roots to rot.
- Over fertilising which causes salt burn of the roots through osmosis, drawing water out of the roots and into the soil, effectively drying the roots and killing them.
When the roots become permanently damaged, there isn’t enough roots to support all the leaves on the tree, so leaves usually start dropping soon afterwards. This kind of root damage and leaf loss can weaken or kill a tree.
Another possible cause is physical damage to the tree, such as:
- Large areas of bark damage on the trunk of the tree, caused by rats or rabbits gnawing on the bark, careless use of powered garden tools such as brush-cutters and line-trimmers, sunburn from extreme midday to afternoon sun causing the bark to burn and peel off (usually on the NW side in the southern hemisphere, and the SW side in the northern hemisphere).
- Root damage caused by digging around the root zone of the tree, or scratching by chickens, which causes damage to the shallow surface feeder roots of citrus.
- Ringbarking caused by piling up mulch around the base of the trunk of the tree, which causes the bark to rot.
Diagnosing Leaf Curling Problems in Citrus
A problem can’t be treated without first figuring what the cause of the problem is. The best way to figure out if a tree has run dry, or is waterlogged, is by using a garden trowel (small hand spade), pushing the blade its full length into the soil, pulling it back, and observing the soil beneath.
In the article – Citrus Problems – Why Is My Citrus Tree Dying? we also discuss other forms of leaf curling, and the various solutions to all these problems in detail.
The relevant solution sections can be viewed directly through the following links:
- How to Prevent Citrus Root Rot
- Avoiding Fertiliser Root Burn of Citrus Trees
- How to Protect Citrus Tree Roots from Chickens
- What Plants Can Be Safely Grown Under Citrus Trees?
By the way, to clear any doubts, the title photograph was created by separating citrus leaves from their roots by pruning a branch off the tree. After a few minutes, the leaves naturally curled along their length. If the cut branch was placed in a vase filled with water immediately after pruning it off, and it was kept out of harsh sun or strong wind, the leaves would not have curled.
Minimising and Repairing Citrus Root Damage
When leaves curl longitudinally in most plants or trees, including citrus, it’s usually a sign of root damage. The earlier that action is taken to remedy the situation, the greater the chances of minimising any permanent damage and helping the plant fully recover.
If roots have died back for whatever reason, they can be induced to grow back by watering with seaweed extract.
Seaweed extract contains almost every mineral, which helps boost plant health very quickly, and it also contains various hormones which act as growth stimulants for plants. The main hormones in seaweed are auxins, gibbelerins, cytokinins and betaines. The cytokinins are root growth stimulants which assist in the regrowth of new roots.
For general transplanting and planting, the recommended application rate is 30mL of seaweed extract into a 9 litre (2 gallon) watering can, applied to the soil at planting time, then again 1 week later.
When dealing with stressed trees, the recommended application rate is 100mL of seaweed extract into a 9 litre (2 gallon) watering can, applied to the soil, around the dripline (edge of the canopy) of tree. Apply monthly until the tree recovers.
Other articles on citrus problems and how to fix them:
- Citrus Problems – Why Citrus Fruit Drops and Flowers Fail to Develop
- Citrus Nutrient Deficiency – Yellow Leaves
- Citrus Problems – Why Citrus Fruit Splitting Occurs and How To Prevent It
- Citrus Nutrient Deficiency – Yellow Leaf with Green Veins
- Citrus Problems – Citrus Yellow Veins on Green Leaf in Winter
- Citrus Problems – Citrus Fruit Has Thick Peel and Hollow Core
- Citrus Problems – How to Control Citrus Gall Wasp, Methods That Work
- Citrus Problems – Why Is My Citrus Tree Dying?
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